1. Field of the Invention
The present invention relates to an enzyme-containing granulated product having improved stability, and more particularly to an enzyme-containing granulated product that undergoes only minimal reduction in activity even in the presence of peroxides typified by bleaching agents. The invention also relates to methods for preparing such products as well as to bleach compositions and detergent compositions containing the product.
2. Description of the Related Art
Detergents and bleaches for clothing frequently contain a variety of enzymes, in addition to surfactants or bleaching ingredients, in an effort to improve detergent power. These enzymes are usually incorporated in the form of granules so as not to lose their activity during storage and to sufficiently exhibit their activities during washing. The enzymatic stability of such enzyme-containing granulated products decreases when the granulated products are blended with bleaching agents, surfactants, builders for detergents, or similar materials. In particular, it is known that enzyme activity decreases considerably when a granulated product is blended with a bleaching agent.
Measures to prevent the reduction of enzyme activity of enzyme-containing granulated products are disclosed by Japanese Patent Application Laid-Open (kokai) No. 62-79298, which describes an enzyme composition in which the core part containing an enzyme is coated with a protective layer containing an alkaline buffering salt of pH 7-11,and by Japanese Patent Application Laid-Open (kokai) No. 3-149298, which describes a bleaching agent containing hydrase particles, in which the enzyme nuclei are coated with a protective agent such as a water-soluble alkali metal silicate, a transition metal, or a reducing agent.
However, those conventional methods for stabilizing enzymes have a problem in that when the thickness of the coating layer is increased or a large amount of a water-soluble substance is incorporated into the coatings so as to fully stabilize the enzymes, the enzyme-containing granulated products come to have reduced solubility in water, and therefore the detergent power of enzymes cannot be sufficiently exerted during use in washing. On the other hand, when the thickness of the coating layer is reduced for the purpose of solubility, the enzymes cannot be satisfactorily stabilized.
Under the above circumstances, the present inventors conducted a variety of studies regarding means for stabilizing enzymes, and found that, so far as enzymes, such as hydrolase, are concerned, the copresence, in a uniformly dispersed state, of such an enzyme, and a stabilizing agent, such as a reducing agent or an antioxidant, is effective in avoiding deactivation of the enzyme and provides a granulated product having excellent solubility. This is surprising because in the past, it has been customary in the preparation of such a granulated product to separate an enzyme from a reducing agent by the use of a coating or the like. The present invention was accomplished based on this finding.